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17 Dec 2017 23:40

On a geological timescale VEI 8 eruptions are fairly common on Earth, and I wouldn't say that they decimate Earth in any way.
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20 Dec 2017 01:07

What do we mean by decimating Earth?  As a planetary object it of course remains intact, but characteristics of its surface, atmosphere, and biosphere can change dramatically.

Volcanic eruptions usually don't affect the biosphere too much -- typically there is a short period of global cooling and decrease in sunlight at the surface until the aerosols precipitate out.  It may affect the food web, but the ecosystem bounces back without difficulty.  Usually just a few years for recovery.

But one enormous exception to this happened at the Permian-Triassic boundary 252 million years ago, which is also the most massive extinction event in the record.  The exact causes of the extinction are quite complex and still being studied, but what is known is that there was a significant eruption of flood basalts in Siberia.  The timing of the eruption correlates very well with the extinction period, and the expected consequences fit pretty well with the pattern of extinction.

In the current leading model, the eruptions had an immediate cooling effect by injecting ash and aerosols in the atmosphere (some portion of the eruptions were pyroclastic.)  As usual this would have some effect on the food chain, but the extinction pattern doesn't strongly reflect this.

The more significant long term effects came from the injection of carbon into the atmosphere, either directly by the eruption or indirectly by vaporizing coal beds or carbonate rocks. Either way, there was a large pulse of atmospheric carbon (reflecting the observed pattern of greater extinction to organisms with lower tolerance to high CO2 levels), which warmed the planet (causing extinction by thermal stresses) and acidified the oceans (causing extinction of organisms with carbonate shells).  The high temperature, high CO2 environment then lead to an ocean anoxia event, which would explain further the pulse of extinction to marine life.

Altogether, this series of events led to the extinction of 96% of all marine species and 70% of terrestrial vertebrates.  More than half of all families died out.  It was the worst die-off known in Earth history, and it was also followed by the slowest recovery period.  Dark days for planet Earth.


PlutonianEmpire wrote:
Source of the post Alternatively, does the presence of advanced multicell life, or lack thereof, alter how a VEI +8 eruption will affect a Terra planet, in any way, shape, or form?


Probably not too much.  The eruption still has the same immediate effect on the atmosphere and climate, and would be expected to leave approximately the same geologic evidence behind in the longer term.  One obvious difference is that there would be no appreciable oxygen in the atmosphere, but I don't think that really changes things too much in terms of effects of an eruption.  A more subtle difference is that without life there is no easy material to burn -- no forests or grasslands, no coal beds to vaporize -- so one of the possible sources of CO2 in the atmosphere as in the above interpretation of End-Permian extinction would not have happened.  

This also plays into consequences of an asteroid strike, or a nuclear war.  Without plants, you remove a significant source of soot from being introduced to the atmosphere, so you avoid much of the nuclear winter.
 
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20 Dec 2017 11:31

Wow, that makes sense, thank you!
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26 Dec 2017 01:25

Quantum computers seem to have made it through the proof of concept phase.  Given the different interpretations of the quantum world which have existed for many decades - does quantum computing change what interpretation to favour?

If we assume the multiverse interpretation, what does that make quantum computers?  Perhaps a device that not only let us express certain problems as a branching point for the universe, but a device that also let us select the preferred branch of reality [the one with the solution that we want]?
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30 Dec 2017 22:21

[quote="Gnargenox"]Might as well add Dark Matter then too :) We have recently seen Rouge Black Holes as well. They would need to have a velocity added to them, since that is a requirement to actually leave the Galaxy.[/quote]

dark matter is just stuff that astronomers haven't accounted for. lol
 
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30 Dec 2017 23:27

greenhand wrote:
Source of the post dark matter is just stuff that astronomers haven't accounted for.

The consensus among astronomers is that it is a different type of matter that only interacts gravitationally, as this model best fits the data and has had the best predictive skill.  There are not enough brown dwarfs, stellar remnants, rogue planets, or other ordinary objects that can otherwise explain it.

Dark matter could be rendered on a galactic scale as a diffuse halo in which galaxies and clusters are embedded, such as shown here for the Bullet Cluster (whereas hot gas is in pink), and as filaments forming the cosmic web like shown here in a cosmological simulation.  

It could also be a population of primordial black holes with a particular range of masses, though in practice this would appear essentially the same since individual primordial black holes in this range would be nearly impossible to locate.
 
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31 Dec 2017 00:09

I really doubt that they can see or detect something that's the size of a basket ball a lightyear away, let alone 300k lightyears.
 
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31 Dec 2017 00:15

I should probably preface this with, an IMO..  sorry, I just tend to blurt things out without being polite.  I'm kinda weird that way.
 
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31 Dec 2017 06:11

We were just talking about how Gravitational wave detection is improving to the point we will possibly be able to use it to detect exoplanets, without the need of involving the host star in our measurements. Who knows, basketballs might not be far behind.

So, has everybody given up on the idea that Galactic rotation anomalies and even gravitational lensing caused by Dark Matter is actually due to the effect of (3) extra dimensions, and the effects these have on gravity in our world? Gravity being changed in our 3 dimensions somehow over astronomical distances.

The idea being, I assume, that these near infinitesimal extra dimensional pockets move around along with normal matter in galactic clusters, accelerating more so in more massive clusters and thereby actually spend less time near each other. This would have less effect in dwarf galaxies as well as have less effect on gravity as you move away from the center of galaxies, which would explain galactic rotation differences. Sounds like as much fudge as anything else, to me.

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31 Dec 2017 16:09

greenhand wrote:
Source of the post I really doubt that they can see or detect something that's the size of a basket ball a lightyear away, let alone 300k lightyears.

If dark matter is regular matter with the size of basketballs, then they would betray their presence by their sheer numbers.  Remember there is about 5 times more dark matter than regular matter, and if you put that into the form of basketballs... then you need a lot of them. :)

Added:  To put numbers behind that, as basketballs there must be on average one of them in every volume of space of about 200 Jupiters.  One would intersect the Earth at least once a year, and one would pass within geostationary orbit at least once a week.  These would be observable by current space debris monitoring systems, and distinguishable from Near Earth Asteroids by their velocities.

The lack of observation of such objects directly, and other observational constraints such as number of gravitational microlensing events, places fairly strict limits on the range of masses that dark matter -- as a form of regular matter -- can have.
 
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31 Dec 2017 16:53

Gnargenox wrote:
Source of the post We were just talking about how Gravitational wave detection is improving to the point we will possibly be able to use it to detect exoplanets, without the need of involving the host star in our measurements.

Yes, possibly, but not for a long while.  The best of the next generations of planned detectors are still a few orders of magnitude too insensitive to pick up even the combined gravitational wave noise from all planets in the galaxy summed together. Picking individual signals out of that noise is also a very challenging problem of signal processing, and I'm not sure if it's practically solvable.

Detecting regular matter objects with masses of basketballs by this method is effectively impossible.  First because it would again not be individual signals, but a collective noise from all of them, which will be many orders of magnitude weaker than a large number of other sources of gravitational wave background noise. But an even deeper problem is that these objects would emit gravitational waves with a period governed by the period of their orbit around the galaxy, rather than around stars or compact binaries.  In other words, they would have hopelessly long wavelengths!

Gnargenox wrote:
Source of the post So, has everybody given up on the idea that Galactic rotation anomalies and even gravitational lensing caused by Dark Matter is actually due to the effect of (3) extra dimensions, and the effects these have on gravity in our world? Gravity being changed in our 3 dimensions somehow over astronomical distances.

This is an example of a modified gravity model.  While such models can be made to work for explaining galactic rotation curves, they have largely fallen out of favor in the last decade or so, in large part due to observations of the Bullet cluster, which showed that gravitational anomalies cannot be attributed to the known distribution of regular matter.  Velocity dispersion in galactic clusters also yields this result -- that the gravitational anomalies really do look like a distribution of nonluminous matter which is distinct from the stars and the gas.

This is not to say scientists are not still working on developing and testing modified gravity models, but functionally the astronomical community is following the LCDM model.
 
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05 Jan 2018 12:43

Why is it so hard for people to determine what alien civilizations, evolution, and life would be like? Seems pretty straight forwards. If you don't know what it will exactly be, then it could be anything, but if it can't be anything, then you can determine what it is by what it is not. So alien life would not be certain things, like a block of solid elemental iron suspended freely, that is not alive. So by working at it that way you can determine that alien life requires a dynamic process and a balance between entropic systems and low entropic systems. It has to change over time. Evolution is easy, it comes from survivability, potential, necessity, competition, and so on... If a world consisted of a green sludge that was immortal and out competes everything, evolution does not take place. Life is its own razor, it doesn't completely stop itself from doing certain things, but it doesn't let it go willy nilly either. Thats all I have time to write, so I will just leave with the main question: Why is it difficult to determine what aliens will be like if we know what they are not?
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05 Jan 2018 12:52

(Sorry for the double post but I just realized the discussion on gravity above me and I wanted to throw something into it)
Gravity isn't a force, its a property, just like mass. Mass is a property of time, and gravity is the shape of the property, this is why there is time dilation. Gravitational time dilation isn't caused by gravity, it is gravity. The curvature everyone talks about?... What lines are being curved? If its space being curved then when I stand still next to a gravity well, nothing would happen... But there is a line that is always traced, a "velocity" always given, a property always expressed, it's time. Standing next to the gravity well, you are tracing a line through time, and so is the well, but it is a curvature in all of the time "lines" near it, towards it, and thats why you fall. Gravity isn't wrong or different, we are wrong. And I suspect that what we are wrong about is time... Anyways I wouldn't call this an answer, rather a subject of debate that would support or refute an answer, or perhaps create an answer. :)
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05 Jan 2018 12:55

Having a sense of what life cannot be surely helps, but that still leaves a very large and almost completely unexplored region of possibility space, poorly constrained from principles of astrobiology.  I also think looking at the variety of lifeforms that have existed through Earth history is a fairly humbling experience.
 
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05 Jan 2018 13:33

Terran wrote:
Source of the post The curvature everyone talks about?... What lines are being curved? If its space being curved then when I stand still next to a gravity well, nothing would happen...

Both the space and the time are curved.  A manifestation of the time curvature is that clocks at different altitudes tick at different rates.  The manifestation of the spatial curvature is a little less obvious:

Suppose you build a ring in space around the Earth.  You would like to know how large your ring is.  So you walk all the way around it, making measurements with a meterstick, and you find that its circumference is 62831.853km.  Which happens to be 2*pi*10000km.  Nice.  Then, looking down, you see that your friend has built another ring just below you.  He does a similar measurement and reports that his ring has a circumference of 2*pi*9999km.  

How far below you is his ring?

The circumference of a ring is 2 times pi times the radius R, so finding the difference in radius should be easy.  Your ring is at 10,000km, and his is at 9999km, so his ring is just 1km below yours.  Right?

Wrong!  We are safe to say that circumference is 2*pi*R if the geometry of the space is flat.  But the mass of Earth curves the space around it!  The spatial distance between the rings will turn out to be slightly greater than 1km because of this curvature. In fact it will be about 440 nanometers greater than 1km.  Which isn't a huge difference, but it is measurable.  

In Schwarzschild geometry, which describes the space-time around a spherically symmetric mass, this is actually how we define the radial coordinate.  Construct in the imagination a ring or a sphere around the mass, measure its circumference, and then derive the radius as the "reduced circumference", by dividing it by 2pi.  Why go to the trouble of defining radius in this weird way?  Because in general, directly measuring the distance from the center of the gravitating mass is hard (the mass tends to get in the way), and the measurement is impossible for a black hole.

Near more massive and compact objects, the distortion of the space becomes even stronger.  An extreme example: For a ring located at a reduced circumference of r=3km around a 1 solar mass black hole, and another ring located at r=2.999km, the physical distance between those rings is not 1 meter, but 8 meters.  As the shells are brought down to the event horizon, this discrepancy grows to infinity!  

This is one of my favorite consequences of space-time curvature in general relativity. :)  Most are familiar with the time dilation, but space gets warped, too.  There is more space near a compact massive object than meets the eye!

Formulas used:

From the spatial component of the Schwarzschild metric, the infinitesimal proper distance [math] between shells at a reduced circumference [math] is given by 

Image

where dr is the difference in reduced circumference between them.  The formula is valid for small separations dr.

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